An increasing demand for glass fibers for insulation, reinforcement and various other applications has led to an increased demand for suitable molten glass compositions from which such fibers may be made. Molten glass compositions are typically formed from powdered or ground raw materials such as compounds of inorganic oxides, carbonates and nitrates. These powdered materials are melted to form a glass melt of a molten glass composition. When the constituents are completely molten and the composition homogenized, the molten composition is passed to a spinner or bushing for the production of glass fibers.
The individual constituents of the glass composition are generally added to the glass melt in the form of ores or bulk raw materials. These bulk materials quite frequently contain small amounts of impurities or contaminants, including carbon containing compounds and iron (Fe.sup.+2) compounds. To help control the level of carbon and iron containing compounds in the glass melt, sodium sulfate is added. While sodium sulfate helps control the levels of iron and carbon in the glass melt, secondary foam is increased to an undesirably high level in the glass melt by the generation of SO.sub.2 gas.
Processes for reducing foam have been known. U.S. Pat. No. 4,042,410 to Ito teaches a method for defoaming molten slag. Ito throws a molding consisting primarily of an organic material into the molten slag. The molding serves both to generate gas and as a heavy weight which enters the slag simultaneously with its throwing to defoam the slag. However, such a defoaming process would be unsuitable for molten glass compositions as gas generation is increased not reduced.
Accordingly, a need remains for a method for controlling secondary foam in a glass melt by reducing the amount of gas generated in the glass melt.